Add bevy_window::Window options for MacOS

[aecsocket]

Objective

MacOS has some nice options for controlling the window and titlebar to make the content appear much more "immersively" in the window. This PR exposes options for controlling this.

Solution

Adds new fields to Window to control these, with doc comments to explain what they do and that they're MacOS only.

Testing

Tested on a MacOS machine (not my own, I don't have one). That's where the below screenshots were taken.

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Showcase

On MacOS, you now have more options for configuring the window titlebar. You can, for example, make the title bar transparent and only show the window controls. This provides a more "immersive" experience for your rendered content.

Before, only this was possible:

Now, you can create windows like this:

This uses the following bevy_window::Window settings:

fullsize_content_view: true,
titlebar_transparent: true,
titlebar_show_title: false,

Migration Guide

bevy_window::Window now has extra fields for configuring MacOS window settings:

    pub movable_by_window_background: bool,
    pub fullsize_content_view: bool,
    pub has_shadow: bool,
    pub titlebar_shown: bool,
    pub titlebar_transparent: bool,
    pub titlebar_show_title: bool,
    pub titlebar_show_buttons: bool,

Using Window::default keeps the same behaviour as before.

[oxkitsune]

very cool to see this exposed. i tried hacking around this and it wasn't pretty

[clarfonthey]

Seems reasonable. Unfortunate some of these aren't better unified, since they could definitely apply to more than just MacOS, but that's more of a limitation of winit than bevy.